Sheathed heater-wire and method of making same.



R. H. READ. V SHEATHED HEATER WIRE AND-METHOD OF MAKING SAME.

APPLICATION FILED JULY 30, 19M. RENEWED JUNE 9.1917. 1,233,808 PatentedJuly 17, 1917.

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WH P: 660% H. READ, OE 'iJVASHINGTOE-l, DISTRICT OF COL'UIEBIA,ASSEGDTGB TS GEE'ERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

SHEATHED HEATER-WERE AND METHOD OF MlKING messes.

Specification 023 Letters Patent.

Patented July fl Application filed July 30, 1914, Serial No. 854,100.Renewed June 9, 1917. Serial No. 178,892.

To all whom it may concern." 1

Be it known that I, ROBERT E. READ, a citizen of the United States,residing in Washington, the District of Columbia, have invented new'anduseful Improvements in Sheathed lleater Wires and Method of Making Same,of which the following is a speci- V fication.

or oxids were employed as insulation; the

present improvements are designed to cheapen and improve the characterof the product. Asbestos insulation may be ap plied as tape, as abraided orwoven tube, as flock secured to a metal tape, or as cord woundin a plurality of layers; the interstices between the fibers, even whencom: pacted, admit of the presence of air carrying some moisture, whichrenders possible the breaking down or the insulation at lower voltagesthan would be the case if less air were present. One of the features ofthe present improvements is to more effectually exclude air andmoisture, and 'l' fiect this result by filling the pores of the asbestoswith a mineral oxid, such as finely divided silica or alumina. This maybe done mechanically by forcing finely divided mineral powder into thepores of the asbestos, or chemically by soaking the asbestos in a soluble salt and precipitating by a reagent or by heat a mineral residue inthe pores or interstices, then drying out the materia, thereby greatlyreducing the porosity of the asbestos insulation and raising its rupturepoint. @ther features of the invention consist in casting a seamlessmetallic sheath around the asbestos-covered wire and forming awatertight seam of hard solder in a folded metal tape inclosing theasbestos. v

- The invention embodies a sheathed wire of asbestos, preferably in theform of flock l, caused to adhereto the metal by a ii described anddefinitely pointed out in the annexed claims.

in the drawings, Figure 1 shows a wlre covered w1th a plurality oflayers of closely wound asbestos cord. Fig. 2 shows a meth- 0d andapparatus for folding an asbestoscovered metal tape around a core-wire,and mechanically filling the pores with finely divided mineralinsulating powder, and brazing the seam. Fig. 3 shows a method offilling the pores of an asbestos covered wire chemically with silicapowder. 41- shows means for "continuously hard-soldering the seam of ametal tape folded to form a sheath around a resistance wire. Fig. 5shows a methodand apparatus for casting a seamless metal casing orsheath around an asbestos-covered wire. Fig. 6 shows an insulatedterminal for the sheathed element.

Referring in detail to the drawings, 1, Fig. 1, represents very muchmagnified a corewire of any desired material or composition suitable forthe work in hand, if for heating work it should have a high specificresistance; if for conducting work it should be or" high conductingmaterial, such as copper. It should be cted of a proper "age for sowiuthe currentdensity it must carry. t is covered with one or more layers2, 3 of closely wound asbestos cord. 1' r. v 101 elication arse-a236,filed June 5, such a wire inclosed in a sheath; to satisfactorilywithstand con-rnercial lighting voltages a thicker bed of insulation isrequired than is he case in my present improvements, as the pores andinterstices off the asbestos carry some moist air; I greatly reduce thepossibility of entrance of such moist air by filling the pores orinterstices with a min rel orri before inclosing the insulated wire inthe metal sheath.

In Fig. 2 I show a mode of filling tae pores mechanically. As here showna tape i, is provided with a superposed layer of silicate of soda; atape of asbestos might be fed over metal tape without being secured toits face; but in either casethe metal and superposed asbestos are led toa tapering die 5 through which is simultaneously led a core-wire 6 fedaccurately to the center of the die, and as it moves forward with themetal tape it is surrounded with a tube of asbestos separating an outercylindrical sheath which is gradually curled into cylindrical form bythe flaring die forcing the edges closely together in a seam which ismaintained in a right line parallel to the axis by a knife blade ofsteel 7 fixed at the. mouth of the die and projecting radially inward tointercept the edges of the folded tape. A hopper containing finelydivided mineral powder, such as ground flint, is jarred intermittentlyby a hammer, 9, operated by. a continuously rotating actuator 10. Thepowder is thus agitated and caused to feed uniformly as the wire andtape are led through the die and forms an evenly distributed annularlayer around the -wire and between it and the asbestos. A s the partsare fed to the right, the tape is closed into a tube with a closed seam,which is held from gaping open under heat, when soldered, by thediepressure, and melted hard solder is applied from a small reservoir 11supported on the die and having an opening in the bottom so that thesolder bathes the edges of the seam. The solder ,is maintained fluid byan insulated heater wire 12 supplied with current-from any suitablesource. The reservoir has heat insulating walls, 13, to conserve theheat, and the wire which forms the while an annular layer of the powderlies around the core-wire. The sheathed wire is then carried throughsmaller dies which reduce its cross-section and force more of the powder,into the pores and interstices and further compact the asbestos untilit is an eficient thermal-conductor which will carry away the heat fromthe core-wire and distribute v1t to any work to which the wire isappliedby means of the inclosing' metal sheath. A wire thus insulated carriesvEry little moist air, especially when the powder 8 with which thehopper is filled is brought hot from an oven where it' is previouslyheated. Other oxide or insulating compounds which are heat-refractoryinsulators may be used, as for example alumina, but finely divided flintis a desirable material as it is cheap, of high insulating value,

. highly heat refractory, and does not become temperatures.

In Fig. 3 I have shown a method of chemically filling the pores of theasbestos with finely divided powder. The treatment may be applied to theasbestos flock, cord, ortape in bulk before the asbestos is applied tothe wire, but inasmuch as many high resistance alloys, such for exampleas nickel-chromium, nickel-manganese, are not afi'ected by weak acidsthe treatment may be applied after the wire is wound or braided withasbestos-Land then led to the tanks of Fig. 3. It is guided over rollersin the tanks, as shown, passing first through a bath 14 containing astrong watery solution of suitable metal salt by which the covering issoaked; it is then led through a second bath, 15, if the silicate isused, in which is contained a weak acid, for example hydrochloric acid,by which the silica is precipitated in the pores as a bulky precipitateof gelatinous silica; thence it may be passed through abath of water intank 16 in which the soluble 'chlorid is washed out, leaving purevgelatinous silica in} the pores and interstices. Thence it passesthrough a tubular electric or other heater,

16 in which the fiber and'sili ca is .dried,

etc.,

from which it emerges as an asbestos-covered wire filled with a densedepositof finely divided dry silica of high'lnsulatmg value. Instead oftreating with silicate of soda other minerals may be employed, forexample a watery bath of ammonia alum may be used, and the soaked wireled through the drier and heater and raised to a red heat, which willbreak up the salt and leave a deposit of finely divided alumina in thepores of the asbestos. Other salts might be used to leave a differentdeposit of insulating material in the pores; I prefer the silica onaccount of its cheapness of production and its excellent thermal andinsulating properties. The covered wire as thus treated may be passedthrough a die, Fig. 4 in .which a metal tape 17 is fed and curled aroundthe asbestos-covered wire, a. steel blade 7 being inserted radially inthe mouth of the die to keep the seam straight, as in Fig. A melting potelectrically heated and mmlated against leakage of heat ismounted overthe die similarly to Fig. 2, the molten bath having access to the seamas indicated. Theseam is held tightly closed and cannot gape open. Ifdesired, the edges of the metal tape may have applied a suitable fluxbefore entering the die 5. When the wire leaves the die the seam isbrazed or hardsoldered; it is then reduced in section in dies, rolls oraswaging machine in ordinary ways until the wire has the desiredfineness, when the insulation will be a hard, compact mass of goodtherinaland electrical insulating value. The brazing heat raises thewire to an annealing temperature and ex els any air trapped in theasbestos and silica. The seamed wire may be slipped into a looselyfitting seamless metal tube which can be then shrunk tight upon it bydies or other reducing means, and circuit terminals made as hereinafterdescribed.

In Fig. 5 I have illustrated a mode of casting a seamless sheath aroundthe asbestos-covered wire. The covered wire 3 is led vertically betweentwo grooved castiron rolls 18, 18 each of which has a semicirculargroove in its periphery. The rolls are hollow and provided with hollowtrunnions mounted to turn in a support 19, and cold water or air is ledthrough an induc tion pipe 20 fixed to the support 19, suitable packingbeing applied at the joint of the induction pipe with the tubulartrunnions 21, 21 The inner end of the pipe 20 projects to the middle ofthe imaginary axis of the hollow roll, its end being closed with a caphaving four. small jet-pipes 22 leading close to the wall of the groovedroll. Thus as the rolls are turned by suitable gearing, cold air orwater is led, as shown by the arrow a into the interior of the left-handroll and discharged in four streams against its inner wall keeping itsufiiciently cool to chill the fluid metal; the air or water is carriedout through a hollow trunnion on the front side of the left-hand rolland through a coupling to the front tubular trunnion of the right-handroll, and thence by similar 'shown in Fig. 5 are much jet-pipes 23 isdischarged against the wall of the righthand roll from which it passesout of the hollow trunnion on the rear of the right-hand roll to theeduction pipe 24. The metal, as for example low brass, is delivered froma melting pot 25 by a valve 26 in a small stream to a soapstone funnel28, which may be lined inside and outside with asbestos, through whichit falls into the closed space between the asbestos-covered wire and theabutting edges of the semicircularly grooved rolls; it is quicklychilled by the relatively cool walls of the rolls, and this action isaided by the jets of cold air delivered upwardly in nozzles 27. Therolls may be superficially oxidized in the grooves to more completelyguard against adhesion of molten metal, The speed of the rolls will varyaccording to the specific heat and thermal conductivity of theparticularmetal.

being cast; with very heavy metals of low specific heat the speed willbe higher than with lighter metals, and the speed of travel is adjustedwith reference to these characteristics of the metal used and thechilling effect of the rolls; as fast as the metal freezes into a solidor pasty form it will leave the rolls and is thence delivered to anysuitable reducing apparatus, such as rolls, dies, or a small swagingmachine to compact the sheath on the asbestos. The proportions magnifiedas the sheath is not more than from one thirtysecond to one sixty-fourthinch in thickness. The wire as thus described may be made of indefinitelength from which any desired length may be cut off for use intranslating devices. As the core wire is not reduced in section, thereducing operations described serving only to compact the sheath intogood thermal relation to the asbestos, the specific resistance of theoriginal wire is the same; therefore it may be accurately predeterminedand the length needed for any use ascertained. T

In Fig. 6 I have shown a terminal connection for the wire. Whencompleted the wire is gripped in a hollow chuck with a tubular handle,somewhat like a pin-vise, and a circular knife revolved around it untilthe sheath is severed. The section of sheath cut off and the asbestosare stripped ofit at each end of the element and a copper tube 29adapted just to fit the core-wire is slipped over its exposed part ateach end of the element; a copper wire 30 to form a lead wire to abinding post or circuit-terminal is then inserted in the end of thecopper tube and a steel countersink is struck with a hammer to indentthe tube at two points 81 to interlock mechanically the tube and thecore-wire. The upset metal forms an effective joint which maintains goodthermal relation and prevents accidental detachment of the lead.

.A piece of braided asbestos tubing 32 is then slipped over the jointand a tubular copper cap 38 pushed over the asbestos and over the end ofthe sheath. The joint with the sheath is brazed as at 35 and fireproofcement applied around the end of the copper lead against the flange andthe asbestos. The cement applied at 34 should be of a kind which willharden under heat, should be fireproof and should not h ve muchshrinkage; I have found a paste made of powdered flint and a weaksolution-of silica of soda very effective; it adheres tenaciously to theparts, and when hardened in a small flame is converted into strong stoneand is water and fireproof.

Having thus described my invention what T claim as new and desire tosecure by Letters-Patent is z- 1. A sheathed wire consisting of aninterior conductor, a bed of heat refractory insulation around theconductor, and a metallic sheath around the insulation, the pores of theinsulation being filled with a heat-refractory finely divided material.

2. A sheathed wire consisting of an interior conductor, a bed ofasbestos around the conductor having its pores filled with finelydivided mineral insulation, and a metallic' sheath around the asbestosin good thermal relation to the conductor.

3. A sheathed wire consisting of an interior conductor, a bed ofasbestos around the conductor having its pores filled with finelydivided mineral insulation, and a seamless metallic sheath around theasbestos in good thermal relation to the conductor.

4. A sheathed wire consisting of an in- I terior conductor, a bed ofasbestos around the conductor, and a bed of mineral insulation betweenthe conductor and the asbestos.

5. A sheathed wire consisting of an in terior conductor, a bed ofheat-refractory insulation around the same, a metallic sheath embracingthe insulation in good thermal relation to the conductor, and a terminaljoint.

Within the insulation consisting of a metal tube mechanicallyinterlocked with the core and a good conducting lead wire projectingfrom the ends of the sheathed wire.

6. A sheathed wire consisting of an interior conductor, a bed of heatrefractory insulation around the same, a metallic sheath inclosing theinsulation in good thermal rev lation to the conductor, a terminal jointwithin the insulation consisting of a metal tube mechanicallyinterlocked with the conductor, and a good conducting lead wire,

and a metallic cap of good heat radiating capacity surrounding the jointand secured to the sheath.

7. The process of making a sheathed resistance element, consisting incovering the conductor with asbestos insulation, and in- ,troducing intothe pores of the asbestos finely divided mineral insulation.

' 8. The process of making a sheathed resistance element consisting incovering the conductor with a surrounding bed of asbestos, anddepositing in the pores of the asbestos fireproof insulating powder.

9. The process of makinga sheathed resistance element, vconsisting incovering a conductor with a surrounding bed of asbestos, andprecipitating within the pores of the asbestos heat-refractoryinsulating powder.

10. The process'of making a sheathed resistance element, consisting incovering a conductor with a surrounding bed of asbestos, filling thepores of the asbestos with masses a heat refractory insulating powder,and surrounding the insulation with a metallic sheath.

11. The process of making a sheathed resistance element, consisting-incovering the conductor. with a surrounding bed of asbestos, fi lling thepores of the asbestos with a heat-refractory insulating powder, and

' casting a seamless metallic sheath around sistance element, consistingin covering the conductor with a surrounding bed, of insulation, feedingit through an opening, supplying molten metal, and chilling the metaluntil solidified within the opening, whereby a seamless metallic sheathis cast around the insulation, and reducing thesection of the castsheath.

14. The method of making a sheathed seamed resistance element,consisting 1n passing a conductor covered with fireproof insulationthrough an opening which holds contracted the seam, and applying fluidmetal continuously to the seam.

15. The method of making a sheathed resistance element,consisting inleading an asbestos-covered wire through vrotating semi-circular walls,supplying molten metal, and chilling the walls continuously while theconductor passes, thereby solidifying a seamless metallic sheath aroundthe conductor.

. ROBERT READ.

Witnesses:

E. B. MGBATH, v v EMILY G. Hroxnr.

